What happened
During cruise flight, the pilots experienced a sudden loud pop followed by severe cyclic control vibration. The crew immediately initiated a precautionary landing to ensure safety.
The investigation
Post-accident examination of the helicopter revealed a fatigue crack in the trailing edge of the blue main rotor yoke flexure, part number 412-010-101-113. The helicopter and the fixture had accumulated 1071 hours of flight time at the time of the incident.
Findings
The failed component was well within its operational life limit, which is set at 5000 hours. The fatigue failure occurred significantly before the scheduled replacement or inspection interval dictated by the life limit.